This invention relates to the art of tufting and more particularly to a method of forming a loop pile fabric having variations in pile density over selective portions of the fabric, the method utilizing a controlled needle tufting machine.
Controlled needle tufting machines are known in the art for selectively engaging and disengaging, in skip-stitch fashion, various of the needles in accordance with a program during each reciprocatory cycle of the needle driving push rods. Basically these machines render selective needles or groups of needles inoperative while the remainder of the needles are operative to pierce and penetrate the backing fabric upon each stroke of the push rods. Examples of such machines are illustrated in U.S. Pat. Nos. 3,115,856; 3,259,088; 3,881,432 and 3,986,465. Such machines, which have been very successful, especially for producing bed spreads, and in the case of individually controlled needle tufting machines have been widely accepted for overtufting a design into a pretufted fabric, as described in U.S. Pat. No. 4,693,190, have only been used to form cut pile fabric wherein the loops formed by the operative needles are cut by respective knives acting beneath the bed of the machine in conjunction with the loop seizing hook. There are two basic reasons for this. The first is because if loop pile were being formed the backstitch normally would be excessively long after an operative needle was subsequently rendered inoperative for a number of subsequent cycles and then rendered operative again. The second is because the previously formed loops would be pulled from the fabric when the needle is rendered inoperative.
For example, in conventional tufting machines the yarn sewn by a particular needle is continuous in that the backstitches are connected together between successive penetrations of the needle into the backing. This is true whether forming loop pile or cut pile, the difference being that in cut pile the loops are cut by the knife acting in conjunction with the loop seizing hook, and this cutting occurs substantially at the center of a loop, and generally there are approximately four such loops on a hook and the cutting for each cycle occurs in regard to the first such loop. Thus, the strand of yarn from the last loop extends back through the needle eye to the yarn feeding means. In a controlled needle tufting machine, however, when a particular needle is held inoperative, the backstitch, unless cut, would extend from the last penetration of the needle while operative to the subsequent penetration which may not occur for a substantial number of cycles. This not only is a waste of yarn but also could result in interlocking of the yarn from a nonoperative needle with the yarn from an adjacent operative needle when it penetrates the backing. Additionally, since only those needles which are stitching are consuming yarn, the amount of yarn on the backstitch side of the backing would be excessive, whether the machine were of the cut pile or loop pile type. For this reason a special yarn clamping device is used which grips and pulls yarn directly from the creel or other yarn storage device on the downstroke of an operative needle, but slips over the yarn on the upstroke and is ineffective when the needle is inoperative.
When forming cut pile on a controlled needle machine when a loop of yarn is cut on the last stitch formed by an operative needle which is thereafter rendered inoperative for a number of cycles, the strand of yarn which remains extending through the needle eye while the needle is inoperative is unattached to any other tufts previously formed. The initial loop thereafter formed when the needle is again rendered operative is not locked into the backing, and is subsequently extracted by a "tail picker" subsequent to the cutting of the loop. Thus, for cut pile fabric the amount of yarn on the backstitch side of the backing material is minimized. If using such a clamp for a loop pile needle which is inoperative for a number of cycles, when the needle is again operatively engaged the yarn not only would be pulled from the creel, but would also be pulled from the last loops since the yarn would extend from the loop back through the needle eye to the creel. Consequently, the pile height of the last few loops formed would be reduced, and this reduction would probably occur nonproportionally in the few loops. Accordingly, such machines have not been utilized to form loop pile fabrics.
The tufting industry has progressively evolved through innovations directed toward duplicating, or at least simulating products which previously were only produced by weaving on a loom. As such products have evolved, because of the substantially higher production rates of the tufting process relative to weaving, more universal availability of the products has resulted. There are, however, certain types of patterns which are currently produced by looms that have not been simulated by tufting. The controlled needle machine, especially the individually controlled needle machines wherein each needle can be selectively controlled to stitch or not stitch, offers the potential of producing a type of product not now produced except by looms. One such product is a carpet having a density variation in various selective portions of the fabric. It is doubtful whether if produced by a controlled needle tufting machine such density variation would be effective visibly if produced utilizing cut pile, but a loop pile product would provide the desired look.